This invention relates generally to riveting and more particularly to a riveting system and a process for forming a riveted joint.
It is well known to join two or more sheets of metal with a rivet. It is also known to use self-piercing rivets that do not require a pre-punched hole. Such self-piercing or punch rivet connections can be made using a solid rivet or a hollow rivet.
A punch rivet connection is conventionally formed with a solid rivet by placing the parts to be joined on a die. The parts to be joined are clamped between a hollow clamp and the die. A plunger punches the rivet through the workpieces such that the rivet punches a hole in the parts thereby rendering pre-punching unnecessary. Once the rivet has penetrated the parts to be joined, the clamp presses the parts against the die, which includes a ferrule. The force of the clamp and the geometry of the die result in plastic deformation of the die-side part to be joined thereby causing the deformed part to partially flow into an annular groove in the punch rivet. This solid rivet is not deformed.
Traditionally, hydraulically operated joining devices are used to form such punch rivet connections. More specifically, the punching plunger is actuated by a hydraulic cylinder unit. The cost of producing such joining devices is relatively high and process controls for achieving high quality punch rivet connections has been found to be problematic. In particular, hydraulically operated joining devices are subject to variations in the force exerted by the plunger owing to changes in viscosity. Such viscosity changes of the hydraulic medium are substantially dependent on temperature. A further drawback of hydraulically operated joining devices is that the hydraulic medium, often oil, has a hydroscopic affect thereby requiring exchange of the hydraulic fluid at predetermined time intervals. Moreover, many hydraulic systems are prone to hydraulic fluid leakage thereby creating a messy work environment in the manufacturing plant.
When forming a punch connection or joint with a hollow rivet, as well as a semi-hollow rivet, the plunger and punch cause the hollow rivet to penetrate the plunger-side part to be joined and partially penetrate into the die-side part to be joined. The die is designed to cause the die-side part and rivet to be deformed into a closing head. An example of such a joined device for forming a punch rivet connection with a hollow rivet is disclosed in DE 44 19 065 A1. Hydraulically operating joining devices are also used for producing a punch rivet connection with a hollow rivet.
Furthermore, rivet feeder units having rotary drums and escapement mechanisms have been traditionally used. Additionally, it is known to use linear slides to couple riveting tools to robots.
It is also known to employ a computer system for monitoring various characteristics of a blind rivet setting system. For example, reference should be made to U.S. Pat. No. 5,661,887 entitled xe2x80x9cBlind Rivet Set Verification System and Methodxe2x80x9d which issued to Byrne et al. on Sep. 2, 1997, and U.S. Pat. No. 5,666,710 entitled xe2x80x9cBlind Rivet Setting System and Method for Setting a Blind Rivet Then Verifying the Correctness of the Setxe2x80x9d which issued to Weber et al. on Sep. 16, 1997. Both of these U.S. patents are incorporated by reference herein.
In accordance with the present invention, a riveting system is operable to join two or more workpieces with a rivet. In another aspect of the present invention, a self-piercing rivet is employed. A further aspect of the present invention uses a self-piercing rivet which does not fully penetrate the die-side workpiece in an acceptable joint. Still another aspect of the present invention employs an electronic control unit and one or more sensors to determine a riveting characteristic and/or an actuator characteristic. In still another aspect of the present invention, an electric motor is used to drive a nut and spindle drive transmission which converts rotary actuator motion to linear rivet setting motion. In yet another aspect of the present invention, multiple rivet feeders can selectively provide differing types of rivets to a single riveting tool. Unique software employed to control the riveting machine is also used in another aspect of the present invention. A method of operating a riveting system is also provided.
The riveting system of the present invention is advantageous over conventional devices in that the present invention employs a very compact and mechanically efficient rotational-to-linear motion drive transmission. Furthermore, the present invention advantageously employs an electric motor to actuate the riveting punch thereby providing higher accuracy, less spilled fluid mess, lower maintenance, less energy, lower noise and less temperature induced variations as compared to traditional hydraulic drive machines. Moreover, the electronic control system and software employed with the present invention riveting system ensure essentially real time quality control and monitoring of the rivet, riveted joint, workpiece characteristics, actuator power consumption and/or actuator power output characteristics, as well as collecting and comparing historical processing trends using the sensed data.
The riveting system and self-piercing hollow rivet employed therewith, advantageously provide a high quality and repeatable riveted joint that is essentially flush with the punch-side workpiece outer surface without completely piercing through the die-side workpiece. The real-time characteristics of the rivet, joint and workpieces are used in an advantageous manner to ensure the desired quality of the final product. Furthermore, the performance characteristics may be easily varied or altered by reprogramming software set points, depending upon the specific joint or workpiece to be worked upon, without requiring mechanical alterations in the machinery. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.